Mesogenic bent-shaped nitrooxadiazoles and thiadiazoles

Abstract

The mesomorphism of three series of compounds has been studied. Compounds in Series I [4-nitrobenzoic acid N′-(4′-n-alkoxybenzoyl)hydrazides] were synthesised by the Schotten–Baumann reaction of 4-nitrobenzhydrazide with 4-n-alkoxybenzoyl chloride in dry pyridine. The resulting compounds were cyclised using phosphoryl chloride to give bent-shaped mesogenic 2-(4′-nitrophenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-oxadiazoles (Series II) or, using phosphorus pentasulphide, 2-(4′-nitrophenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-thiadiazoles (Series III). These compounds have been characterised using a combination of elemental analysis and spectroscopic techniques. The mesomorphic properties of the three series were compared with one other and with other structurally related compounds. The effect of different heterocyclic moieties and terminal substituents on mesomorphism has been evaluated.

Keywords:

• nitro group
• oxadiazoles
• thiadiazoles
• bent-shaped
• mesomorphism

Acknowledgements

The authors thank the Dean, Faculty of Technology and Engineering and the Head of the Applied Chemistry Department, University of Baroda, for providing research facilities.